Heat Exchangers transfer heat from a hot area to a cooler area through conduction and convection. Certain forms of Heat Exchangers use tubes within a shell. Other designs may use heat pipes.
For a given amount of heat to transfer there is usually a minimum size of Heat Exchanger. In general, if more heat has to be transferred then a larger Heat Exchanger is needed or one that is more efficient. The amount of heat that may be transferred is the heat transfer coefficient multiplied by the surface area to volume ratio. Another figure of merit for the Heat Exchanger is the pressure drop across the inlet and outlet of a flow through a Heat Exchanger. A typical shell and tube Heat Exchanger has a heat transfer coefficient multiplied by the surface area to volume ratio of 104 to 106 Watts/M3K where K is the temperature in degrees Kelvin. The corresponding pressure drop is 10−3 to 10 Pascals per meter of length. If the surface area to volume ratio is increased then a given Heat Exchanger can transfer more heat for a given size.
In some applications, where the Heat Exchanger also has to support a mechanical load, the Heat Exchanger is simply built large enough for the amount of heat to transfer. When the Heat Exchanger design is constrained by the amount of heat to transfer, the physical size of the Heat Exchanger and the structural requirements of the exchanger, then alternatives are needed. The problem of exchanging a given amount of heat energy in a Heat Exchanger of a given size is solved, at least partially, by using a Heat Exchanger with a greater than typical surface area to volume ratio.
The problem is further complicated if the Heat Exchanger has to support mechanical loads. But this problem may be solved by using a Heat Exchanger with an internal structure, such as a truss structure, capable of supporting mechanical loads as well as having a large surface area to volume ratio.
The use of a truss architecture for active cooling has been reported in literature (for instance, Lu, Valdevit, Evans, “Active cooling by metallic sandwich structures with periodic cores”, Progress in Materials Science 50 (2005) 789-815), incorporated by reference in its entirety. However, the only fabrication methods described are expensive, limited to a single truss layer, and limited to large truss unit cell sizes.
As disclosed in Monro et al. “Topical Review Catching Light In Its Own Trap,” Journal Of Modern Optics, 2001, Vol. 48, No. 2, 191-238, which is incorporated by reference herein in its entirety, some liquid polymers, referred to as photopolymers, undergo a refractive index change during the polymerization process. The refractive index change can lead to a formation of polymer optical waveguides. If a monomer that is photo-sensitive is exposed to light (typically UV) under the right conditions, the initial area of polymerization, such as a small circular area, will “trap” the light and guide it to the tip of the polymerized region, further advancing that polymerized region. This process will continue, leading to the formation of a waveguide structure with approximately the same cross-sectional dimensions along its entire length.
Tian, Wadley, et al. (in “The effects of topology upon fluid-flow and heat-transfer within cellular copper structures”, International Journal of Heat and Mass Transfer volume 47, issues 14-16, July 2004, p. 3171-3186) have experimentally investigated copper ordered cellular materials as heat sinks. The structures described therein are constrained to simple, flat geometries, do not have enhancements for increased convective heat transport, and are not designed to satisfy multiple functions (e.g. structural function in addition to heat transfer function).
As such, there is a need for Heat Exchangers that can support a mechanical load and that have a high surface area to volume ratio, as well as being economical to manufacture.